This invention relates to reaction products of organic polyisocyanates, long-chain alcohols, cyanamide, and ammonia or a volatile amine as neutralizing agent for the cyanamide groups in which the reaction products are free from polyester and polyether groups and halogen atoms.
The suitability of anionically modified polyisocyanate products for the preparation of aqueous dispersions rests on the presence of incorporated ionic centers, more particularly incorporated sulfonate or carboxylate groups. In the preparation of coatings from such dispersions, the ionic centers generally remain in the resultant coatings, resulting in a reduction in the resistance to water of the resulting coating.
In addition, water-dispersible polyisocyanate addition products modified by anionic cyanourea groups are known. Cf. German Offenlegungsschriften 3,441,934, 3,600,595, 3,735,198, 3,813,840, and 4,133,572. Coatings obtained from such dispersions are considerably more resistant to water than coatings obtained from standard PUR dispersions because the hydrophilicizing cyanourea anions acquire a self-crosslinking character after loss of the counterion and thus lose their hydrophilicity on completion of crosslinking.
Resistance to water and a reduction in hydrophilicity inherent in the products is also important in the case of dispersion aids (for example, for paraffins, pigments, polymers).
Whereas tanning agents form chemical bonds with the collagen in leather and are supposed to increase the shrinkage temperature of leather through this crosslinking, so-called retanning materials are auxiliaries that have little or no tanning effect of their own but lead to better dyeability and to greater softness and fullness. Such materials must be capable of penetrating into leather and of dispersing and fixing inter alia oiling agents or vegetable tanning materials therein. Examples of such retanning agents are formaldehyde/naphthalene sulfonic acid condensates, (meth)acrylic acid polymers, (meth)acrylic acid/acrylonitrile copolymers, oligourethanes containing ionic groups (see, for example, U.S. Pat. No. 4,106,897) and dicyanodiamide resins (JALCA, 83, 196 (1988)).
It has now surprisingly been found that when the reaction products of this invention are used as retanning materials, very soft leathers characterized by excellent feel are formed, and the reaction products are absorbed into the leather until the bath is substantially quantitatively exhausted. The required fastness values are obtained surprisingly quickly so that the leather can be further processed without unwanted delay. A major advantage of products of this invention is their reaction in the leather to form a water-insoluble (non-hydrophilic) dimer or oligomer. Accordingly, the products of the invention are not washed out and do not migrate to any significant extent on completion of the reaction.